1. Field of the Invention
This invention relates to fluid power rotary actuators, and in particular to a radial bellcrank actuator.
2. Background of the Invention
Fluid power actuators enjoy considerable popularity in a wide variety of industrial applications, especially in automation and numerical control machines. Either pneumatic or hydraulic fluid may be used to power these actuators.
The most common applications for rotary actuators are in automation where they perform functions such as turning valves, rotating products, positioning diverting arms, bending products, etc. They are also used in animation, process control (primarily valve actuation), vehicle control such as rudders or flaps, robotics, agricultural and other mobile equipment, etc.
A typical rotary fluid power actuator system comprises a cylinder within which a piston is free to reciprocate. A pressurized fluid supply is alternately connected to either a first cylinder end or a second cylinder end through a directional control valve and cylinder ports. The piston is driven away from the cylinder end to which the pressurized fluid supply is connected. A flow control valve may be connected to each cylinder end to control the flow rate of fluid escaping from the cylinder ahead of the piston, which in effect controls the piston speed during most of the stroke.
Means is provided to convert the linear reciprocating motion of the piston into rotary motion of an output shaft, which is attached to the load to be moved. The rotary motion of the output shaft is rotationally reciprocal, and is generally limited to an amount less than one full rotation up to as much as a few rotations, rather than unlimited rotation as in the motion produced by a motor.
In operation, the directional control valve permits fluid at driving pressure to flow into a first cylinder end, which drives the piston towards an opposite, second cylinder end. The speed at which the piston travels toward the second cylinder end (and hence the speed of rotation of the output shaft) may be controlled by the rate at which fluid is allowed to escape from the second cylinder end through the flow valve associated with the second cylinder end.
Fluid power rotary power actuato applications can be divided into categories based on their degree of positioning control. The most basic system moves to stops at each end of a fixed stroke. It is normally controlled by a single valve having two states, one corresponding to each position of the actuator. The speed of motion may be controlled by adjustable metering valves acting on the fluid stream. The torque produced can be controlled by controlling the pressure of the fluid.
At the other end of the positioning control spectrum are infinitely positionable systems in which the fluid driving the actuator is controlled by a proportional or servo valve which is part of an active control system which includes position feedback. These systems require an actuator with little or no lost motion or backlash in order to achieve accuracy.
Between these two extremes are various levels of positioning capability. Some examples are adjustable stops to limit rotation, multiple stops based on additional cylinders integrated into the actuator (generally, each stop requires an additional valve for control), and cushions which decelerate the load near the end of rotation.